1. Technical Field
The present invention relates to lithography processes, and, more particularly, to source-mask optimization methods and systems.
2. Description of the Related Art
Throughout the past 30 years, lithography techniques and capabilities have improved to meet the demand for scaled down devices and corresponding features. For example, the minimum pitch between apertures for a mask has generally reduced about 10% per year. Here, the minimum pitch can be defined as
            min      ⁢                          ⁢      pitch        =                  2        ⁢                                  ⁢                  k          1                ⁢        λ            NA        ,where k1 is a lithographic process complexity factor, λ is the wavelength of the light emitted by the light source, and NA is the numerical aperture of the system. Historically, the minimum pitch has been reduced through optical scaling of
      λ    NA    .For the 22 nm node, the next value of λ that should be used in optical scaling to obtain the minimum pitch accommodating the 22 nm node is approximately 13.5 nm, in the EUV wavelength scale, which is difficult fairly to implement using existing technology.